The present disclosure relates generally to proximity detecting systems and, more particularly, to a non-contact obstacle detection system (for example, a human obstacle) or other objects having similar dielectric properties utilizing ultra sensitive capacitive sensing, such as may be implemented in conjunction with a motor vehicle power lift-gate.
Various systems have been devised for detecting obstacles (e.g., humans) in the path of a moveable panel such as an automotive power window, power sliding door or power hinged door. When an obstacle is detected, forward movement (e.g., closing) of the panel is interrupted and, optionally, the movement of the panel may be thereafter reversed (e.g., opened). These detection systems may generally be characterized as either xe2x80x9ccontactingxe2x80x9d or xe2x80x9cnon-contactingxe2x80x9d. In a contacting system, an obstacle is detected only after some form of physical contact occurs between the panel and the obstacle, and may include devices such as pneumatic/pressure sensitive strips, or possibly sensors responsive to changes in mechanical or electrical loading in the apparatus that moves the panel.
On the other hand, in a non-contacting system, an obstacle is detected before actual contact occurs. One specific type of non-contacting obstacle detection system employs the use of a capacitive element(s) as a proximity sensor(s). Capacitive proximity sensors may include one or more electrical conductors formed along the leading edge of a moveable panel, as well as a capacitance sensitive circuit (e.g., a bridge circuit or an oscillator) coupled to the conductor(s). An obstacle (e.g., a human hand) in proximity to the conductor(s) changes the capacitance of the sensor, which change is thereafter detected by the capacitive sensitive circuit.
Unfortunately, certain difficulties are inherent in creating a sensitive capacitive proximity system that can distinguish between environmental conditions and an actual foreign object. On one hand, the sensors themselves may not be of uniform design and/or sensitivity, or may be subjected to certain environmental conditions (e.g., moisture) that can affect the capacitance value thereof. In addition, certain high frequency components in such capacitance detection systems can result in radiated emissions to neighboring electronic components.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a non-contact obstacle detection system utilizing ultra sensitive capacitive techniques. In an exemplary embodiment, the system includes a sensing element disposed in proximity to a moveable panel and a proximity detection circuit in communication with the sensing element. The proximity detection circuit generates a differential output signal reflective of whether a foreign object is in proximity to the sensing element. In addition, a central control module is in communication with the sensing element. The central control module determines whether the differential output signal is reflective of a foreign object in proximity to the sensing element. If the central control module determines that the differential output signal is reflective of a foreign object in proximity to the sensing element, and the moveable panel is moving toward a closed position, then the central control module generates a control output signal to stop the moveable panel from moving toward the closed position.
In a preferred embodiment, the sensing element further includes a capacitive sensing element having a nominal capacitance, wherein the proximity detection circuit detects a change in the nominal capacitance as a result of a foreign object in proximity to the sensing element. The proximity detection circuit is integrated within the sensing element, and further includes a first oscillator, which generates a first frequency signal. The first frequency signal is dependent upon the capacitance of the sensing element. A second oscillator generates a reference frequency signal, wherein the differential output signal is determined from a comparison between the first frequency signal and the reference frequency signal.
Preferably, the obstacle detection system further includes a coaxial cable coupling the proximity detection circuit and the central control module, the coaxial cable transmitting both a DC power signal and the differential output signal. Both the proximity detection circuit and the central control module further include a bias xe2x80x9cTxe2x80x9d apparatus included therewith.